Canadian National Breast Screening Study-2: 13-Year Results of a Randomized Trial in Women Aged 50-59 Years

Reviewers: Li Liu, MD
Source: Journal of the National Cancer Institute, Volume 92:1490-1499, (September) 2000

Précis: Mammography may not offer survival advantage over annual breast examination

Introduction

There is universal agreement that women 50 to 69 years of age should undergo screening mammography because randomized, controlled trials have shown that such screening reduces breast cancer mortality in this age group (JAMA 1995 Jan 11;273(2):149-54). This consensus is bolstered by the results of cost-effectiveness analyses that consistently show that this benefit can be achieved at a reasonable cost. However, when physical examination is performed in addition to mammogram, the extent to which mammogram contributes to the reduction of mortality in women is unknown. In this randomized study, the researchers compared breast cancer mortality following annual mammogram plus physical examination and physical examination only.

Method

A total of 39,405 women were assigned either to annual physical examination or to examination plus mammography since the mid-1980s.

Results

• At the first screening interval, adding mammography to physical examination appeared to more than double the cancer detection rate, from 3.45 per 1000 per 7.20.
• With longer follow-up, this difference between the two groups has virtually disappeared.
• Tumors detected by mammography plus physical examination were more likely to be small and were less likely to be lymph node-positive.
• There were 88 breast cancer deaths among women who had mammography, compared with 90 breast cancer deaths among women who had only physical examination.

Discussion

In this study, adding mammography to careful annual physical examination had no impact on breast cancer mortality. Annual mammography plus physical examination did appear to have lead-time advantage with more patients detected in earlier stages. Unfortunately, these apparently favorable prognostic findings did not translate into a survival advantage for women screened with mammography plus physical examination. In addition to mammography and physical examination, breast self-examination may also play a positive role in reducing the mortality rate of breast cancer and should be studied in conjunction with mammography and physical examination.